Collaborative Research: Role of Polymer Sequence on Penetrant Transport in Charged Brushes

Molecular-scale brushes, created by grafting polymers to surfaces, can be used to control the properties of the surface, including its charge, wettability, permeability, and response to environmental conditions such as salt concentration. In principle, polymer brush-coated surfaces are potentially transformative technologies for important applications in drug delivery, chemical separation processes, and water purification.

Selectively controlling the transport of small molecules and particles into and out of the brush is necessary for these applications, but the ability to do so remains a persistent challenge because it is difficult to tune the structure of the brush. This research project will develop a route to control brush conformation and its response to environmental conditions by engineering the sequence of monomers that compose the polymer brush.

The team will relate the structure of the engineered brushes to how small molecules and particles move through them under static and flow conditions. This research will address a critical knowledge gap by providing understanding of how the sequence of charged monomers affect the transport of penetrants, leading to improved membrane coatings for water and biologic drug purification.

The project team will disseminate these results to scientists and engineers in Houston’s petrochemical, biomedical, and materials industries through local meetings, including the Texas Soft Matter Meeting. In parallel, they will develop educational outreach videos on water purification in multiple languages spoken in the Houston metro area, and present hands-on demonstrations for the general public at the Houston Energy Festival.

The objective of this project is to develop a fundamental understanding of the influence of polymer sequence on transport within charged polymer brushes. Team members from two nearby universities in Houston will integrate complementary expertise in sequence-controlled polymer synthesis (Marciel – Rice University), neutron scattering applied to brushes (Conrad – University of Houston), and state-of-the-art microscopy techniques (Marciel and Conrad) to address three specific aims: (1) determine the role of polymer sequence on brush properties, (2) identify mechanisms that dictate coupling between penetrant and charged polymer brush dynamics, and (3) understand the effects of flow on out-of-equilibrium penetrant transport in charged polymer brushes.

Protein engineering methodologies will be used to synthesize sequence-controlled charged polymers with isotopic labelling for grazing-incidence small angle neutron scattering (GI-SANS) and neutron reflectivity (NR) experiments to measure brush conformation and height in equilibrium and out-of-equilibrium conditions. Penetrant transport coefficients will be measured using confocal and total internal reflection fluorescence correlation spectroscopy (TIR-FCS), exploiting vertical sensitivity to distinguish transport inside and outside brushes and tested against theories for diffusion and dispersion within polymer matrices and in porous media.

Together, these studies will provide new insight into the role of charge fraction and spacing on the diffusive and flow-driven transport of penetrants in charged brushes, which will pave the way for the design of advanced responsive surfaces.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.